Vehicle stability control device

ABSTRACT

A vehicle stability control device is capable of steering wheels independently of the driver&#39;s handling operation, in which a suitable steering angle parameter in determining a target value for a turning state parameter is selected. The control device calculates a provisional target steering angle for wheels based upon an amount of an operation of a driver and a predetermined steering characteristic; a target value for the turning state parameter; and a target steering angle for wheels for reducing a magnitude of a deviation of the actual turning state parameter from its target value when the magnitude of the deviation is at a reference value or above, and thereby controlling a steering angle based upon the target steering angle. During execution of controlling the steering angle based upon the target steering angle, the target value of the turning state parameter is calculated based upon the provisional target steering angle.

This application is a Continuation of U.S. patent application Ser. No.10/560,779 filed Dec. 14, 2005, issued as U.S. Pat. No. 7,567,863, whichin turn is a National Phase of PCT/JP05/005071 filed Mar. 15, 2005. Thedisclosure of the prior applications is hereby incorporated by referenceherein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for controlling a behavior ofa vehicle such as an automobile (a stability control), and morespecifically, to such a device that stabilizes the running behavior of avehicle by controlling a steering angle of wheels.

2. Description of Prior Art

There have been developed various control devices for stabilizing arunning behavior of a vehicle in its yaw direction through generating acounter yaw moment of suppressing oversteering and understeeringtendencies owing to an imbalance in braking or traction forces in thelateral direction of the vehicle, the saturation of a tire force, etc.Such a counter yaw moment, usually, is generated by controlling the tireforce distribution in a vehicle. Further, in a vehicle equipped with asteering system enabling the steering of wheels independently of adriver's steering action, a counter yaw moment can be generated by anautomatic steering of wheels. Examples of control devices forstabilizing a vehicle behavior through an automatic steering aredisclosed in Japanese Patent Laid-Open Publication No. 5-105055 andJapanese Patent No. 2540742, in which a steering angle of wheels iscontrolled to generate a counter yaw moment against the yaw moment owingto a braking force imbalance between the left and right wheels on avehicle, and thereby ensuring its straight line stability.

In control devices as described above, a degree of deterioration of avehicle behavior, i.e. oversteering and understeering tendencies, ismonitored by comparing an actual or measured value of a parameterindicating a turning state, such as a yaw rate, with the correspondingtarget value determined with operational parameters, such as a steeringangle and a vehicle speed. Then, a counter yaw moment is generated toreduce the difference between the actual and target values of theturning state parameter by adjusting individual braking forces and/orthe steering angle of wheels.

In the above-mentioned control strategies, the execution of theautomatic steering for the stability control alters an actual steeringangle from an angle determined with a driver's steering operation (therotational angle of a steering wheel operated by a driver). Under anextreme condition where a large counter yaw moment is required forstabilizing a vehicle behavior, not only the magnitude but also thedirection of the actual steering angle may be altered from thosedetermined with the driver's steering operation. However, this fact isnot taken into account in conventional control devices as describedabove. In these devices, an actual steering angle is always used fordetermining a target value for the turning state parameter, so that, ifthe actual steering angle is altered by the automatic steering control,the resultant behavior and/or tracking course of the vehicle would bedeviated from those intended by the driver.

Accordingly, conventional vehicle stability control devices as describedabove may be improved to operate more appropriately, taking into accounta steering angle variation under the automatic steering control.

SUMMARY OF INVENTION

According to the present invention, there is provided a novel vehiclestability control device for suppressing oversteering and understeeringtendencies through controlling a steering angle of the vehicle, improvedto execute a stability control more appropriately than ever by selectinga suitable steering angle parameter in determining a target value for aturning state parameter to be controlled.

In one aspect of the present invention, the inventive device may beequipped on a vehicle for controlling its running behavior. A steeringapparatus of the vehicle is adapted to steer a wheel independently of adriver's steering operation. The inventive control device comprises aportion of calculating a target steering angle (provisional) for wheelsbased upon an amount of an operation of a driver, such as a rotationalangle of a steering wheel rotated by a driver, and a predeterminedsteering characteristic; a detector of detecting an actual value of aturning state parameter, such as a yaw rate; and a portion ofcalculating a target value for the turning state parameter. The actualand target values of the turning state parameter are compared with eachother. Then, if the magnitude of the deviation of the actual turningstate parameter from its target value is at a reference value or above,the steering angle is controlled to be a target steering anglecalculated for reducing the deviation of the turning state parameter. Inthis structure, according to the present invention, the target value ofthe turning state parameter during executing an automatic steeringcontrol for stabilizing a behavior is calculated based upon the targetsteering angle (provisional), not the actual one. In other words, aslong as the automatic steering control is executed, the provisionaltarget steering angle, namely the target steering angle determined basedupon an amount of an operation of a driver and a predetermined steeringcharacteristic, is selected as a parameter of a steering angle fordetermining a target turning state parameter.

The target value of the turning state parameter, determined as afunction of a steering angle, determines the tracking course ordirection of the vehicle, so that the driver's intention should bereflected in the target turning state parameter value. However, asnoted, the actual steering angle under the automatic steering control isdetermined through the stability control for suppressing oversteeringand understeering tendencies, so that the actual steering angle wouldnot be completely consistent with the driver's intention. Thus, theprovisional target steering angle determined based upon an amount of anoperation of a driver is used in determining the target turning stateparameter value during executing the automatic steering control.

In addition, it should be noted that the use of the provisional targetsteering angle in determining a target turning state parameter isadvantageous for compensating for a delay in the response of thesteering apparatus, since the resultant target turning state parameteris determined by a parameter not incorporating the delay of the steeringapparatus. (The actual steering angle includes the effect of the delayof the steering apparatus.)

The provisional target steering angle may be calculated as a sum of asteering angle of wheels corresponding to the amount of the operation ofthe driver and a control steering angle for accomplishing apredetermined steering characteristic. In an embodiment, the provisionaltarget steering angle may be determined as a function of a vehiclespeed, and preferably varying with a steering gear ratio determined withthe vehicle speed. The provisional target steering angle is determinede.g. through varying the ratio of the steering amount of wheels to theamount of rotation of the steering wheel (handle) of a driver, dependingupon the vehicle speed.

In the above-mentioned structure, when no steering control of wheelsbased upon the target steering angle is executed, i.e. when the actualsteering angle may be considered as resulting from the driver'soperation without modification through a stability control, the targetvalue of the turning state parameter may be calculated based upon theactual steering angle. Accordingly, in this case, the inventive devicemay comprise a detector of detecting an actual steering angle of wheels.If the magnitude of the deviation of the turning state parameter islower than the reference value, the steering angle of wheels may becontrolled through the steering apparatus based upon the provisionaltarget steering angle.

In the inventive device, the control for stabilizing a vehicle behaviormay be executed through not only the automatic steering but alsoadjusting individual braking and driving forces (tire forces) on therespective wheels. In this case, the inventive devices may furthercomprise a portion of controlling braking and driving forces on therespective wheels; a portion of calculating a total target amount of astability control, such as a counter yaw moment, based upon the turningstate parameter deviation for reducing the magnitude thereof; and aportion of dividing the total target stability control amount intotarget stability control amounts each for steering control of wheels andbraking and driving force control, at a predetermined ratio. In thisdevice, the target steering angle will be calculated based upon thetarget stability control amount of steering control of wheels and usedfor controlling the steering angle of wheels. Braking and driving forceson the respective wheels will be controlled based upon the correspondingtarget values calculated based upon the target stability control amountof braking and driving force control. The dividing of the total targetamount of a stability control into target stability control amounts eachfor steering control of wheels and braking and driving force control maybe done through calculation of yaw moments. It should be noted that, inthe device executing both the automatic steering and adjustingindividual tire forces, the target turning state parameter value will bedetermined as described above, so that the driver's intention isreflected therein.

By the way, when the steering apparatus becomes disabled from steeringthe wheels independently of a driver's steering operation due to anyfailure, no longer automatic steering will be executed. In such a case,the steering angle to be selected in determining the target turningstate parameter may be the actual steering angle (because nomodification of the steering angle is executed for a stability control).Further, the stability control will be executed only through adjustingtire forces on the respective wheels (i.e. the dividing portion assignsthe total target stability control amount only to the target stabilitycontrol amount for braking and driving force control).

In this connection, in accordance with this strategy, the parameter of asteering angle in determining the target turning state will be changedfrom the provisional target steering angle to the actual steering angleif the automatic steering becomes disabled during executing a stabilitycontrol. This change of the parameter of the steering angle would causea stepwise variation in the target turning state parameter, leading to adisturbance in a vehicle running behavior. Thus, the inventive devicemay be designed to reduce the variation in the turning state parameterowing to the change of the steering angle used in calculating the targetturning state parameter from the provisional target steering angle tothe actual steering angle. The degree of the reduction of the variationin the turning state parameter may be larger at a higher vehicle speedthan at a lower vehicle speed because, while the change of the parametershould be done as soon as possible, the disturbance of a behavior in ahigh speed vehicle should be avoided. In an embodiment, a smoothingprocess may be applied for a parameter of steering angle in determiningthe target turning state parameter.

Accordingly, it is an object of the present invention to provide new andnovel vehicle stability control devices for a vehicle, such asautomobile, by generating a counter yaw moment through the steering ofwheels for stabilizing a behavior of the vehicle, taking into accountthat the steering angle could be changed independently of the driver'shandling operation.

It is another object of the present invention to provide such devicesoperating more appropriately than ever by selecting a parameter of asteering angle in determining and controlling a target turning state,depending upon operational conditions.

It is a further object of the present invention to provide such devicesimproved for preventing erroneous operation of the device duringexecuting a stability control.

Other objects and advantages of the present invention will be in partapparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1 is a diagrammatical view of a four wheeled, rear drive vehicleequipped with a turning angle varying apparatus of a semi-steer-by-wiretype serving as an automatic steering apparatus and a vehicle stabilitycontrol device according to the present invention;

FIG. 2 is a flowchart of a vehicle stability control routine executed inthe preferred embodiments in the vehicle in FIG. 1 according to thepresent invention for controlling the steering angle of the left andright front wheels and braking pressures for the respective wheels;

FIG. 3. shows a map of a relation between a vehicle speed V and asteering gear ratio Rg.

FIG. 4 shows a map of a filtering factor R, a function of a vehiclespeed V.

FIG. 5 is a partial flowchart of a modification of the flowchart shownin FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 diagrammatically shows a four-wheeled, rear drive vehicleincorporating a preferred embodiment of a vehicle stability controldevice according to the present invention. In this drawing, a vehiclebody 12 has left and right front wheels 10FL and 10FR, left and rightrear-wheels 10RL, 10RR. As usual, the vehicle is formed to transmit adriving torque or a rotational driving force, outputted from an engine(not shown) according to a throttle valve opening in response to thedepression of an acceleration pedal by a driver, to the rear wheels 10RLand 10 RR through a differential gear system, etc. (not shown).

Front wheels 10FL, 10FR each are steered through tie rods 20L, R with arack-and-pinion-type power-steering device 16 actuated in response tothe rotation of a steering wheel 14 by a driver. For automaticallysteering the wheels, however, the steering device 16 employed here is ofa semi-steer-by-wire type, provided with a turning angle varyingapparatus 24 as an auxiliary steering apparatus which enables thecontrol of the steering angle of the front wheels independently of thedriver's handling.

The turning angle varying apparatus 24 includes a driving motor 32,having a housing 24A, operationally linking to the steering wheel 14 viaan upper steering shaft 22, and a rotor 24B, operationally linking to apinion shaft 30 via a lower steering shaft 26 and a universal joint 28.The driving motor 32 rotates the lower steering shaft 26 relative to theupper steering shaft 22 under the control of an electronic control 34 asdescribed later. If any failure occurs in the rotational driving motionin the apparatus 24, the housing 24A and rotor 24B are mutually,mechanically locked by a locking device (not shown), preventing therelative rotation of the upper and lower steering shafts. Forcontrolling the operation of the turning angle varying apparatus 24, asteering angle θ of the steering wheel 14, i.e. the rotational angle θof the upper steering shaft 22, and a relative angle θre of the lowersteering shaft 26 measured from the upper steering shaft 22 (between thehousing 24A and rotor 24B) are detected with angular sensors 50 and 52,respectively.

The power steering device 16 may be either of hydraulic power steeringtype or of electric power steering type. However, for reducing a torquereaction transmitted from the apparatus 24 to the steering wheel 14during the automatic steering control, preferably employed is arack-coaxial type electric power steering device having a motor and amechanism for converting the motor's rotational torque into a linearmotional force of the rack bar 18.

A braking system 36, generating braking force on each wheel, has ahydraulic circuit 38 comprising a reservoir, an oil pump and variousvalves, etc. (not shown), wheel-cylinders 40FL, 40FR, 40RL and 40RR,equipped on the respective wheels, and a master cylinder 44 actuated inresponse to the depression of a brake pedal 42 by the driver. In thebraking system, a braking pressure in each wheel cylinder, and in turn,the braking force on each wheel, are adjusted through the hydrauliccircuit 38 in response to a master cylinder pressure. The brakingpressure in each wheel cylinder may also be controlled by the electroniccontrol 34 as described later. For controlling the braking pressures,pressure sensors 60 i (i=FL, FR, RL, RR) for detecting the pressures Pbi(i=fl, fr, rl, rr) in the wheel-cylinders 40FR-40RL may be installed.

Electronic controller 34, controlling the turning angle varyingapparatus 24 and the braking pressures (braking force) of the respectivewheels, may be of an ordinary type, including a microcomputer havingCPU, ROM, RAM, and input/output port devices, interconnected with thebidirectional common bus, and drive circuits. As seen from FIG. 1,inputted to the controller 34 are signals of: the steering angle θ ofthe steering wheel 14; the relative angle θre of the lower steeringshaft; a vehicle speed V, detected with a vehicle speed sensor 54, orobtained from wheel velocities Vwi (i=fl, fr, rl and rr are front left,front right, rear left and rear right, respectively) detected with wheelvelocity sensors (not shown); a yaw rate γ, detected with a yaw ratesensor 56; a lateral acceleration Gy, detected with a lateralacceleration sensor 58; and pressures Pbi (i=fl, fr, rl, rr) in thewheel-cylinders 40FR-40RL.

The controller 34 executes a steering gear ratio control and a stabilitycontrol through the automatic steering control and/or adjusting brakingforces or pressures on the respective wheels.

For the steering gear ratio control, the controller 34 controls theturning angle varying apparatus 24 through the rotation of the motor 32to vary a steering gear ratio, i.e. the ratio of the steering angle ofthe front wheels to the rotational angle of the steering wheel 14,providing a predetermined steering characteristic. In operation, first,a steering gear ratio Rg for accomplishing a predetermined steeringcharacteristic is determined in a portion in the controller 34 using amap shown in FIG. 3, based upon a vehicle speed V which may becalculated with the wheel velocities Vwi. Then, a target steering angle(provisional) δst is calculated by:δst=θ/Rg  (1),and the turning angle varying apparatus 24 is actuated to steer thefront wheels, adjusting their steering angle to δst. Thus, in this case,the turning angle varying apparatus 24 functions as a steering gearratio varying apparatus.

In this connection, the target steering angle (provisional) δst isconsidered a sum of the steering angle corresponding to an actual amountof a driver's steering action (a rotational angle of the steering wheel14), equal to θ/Rgo, and a control amount for obtaining a predeterminedcharacteristic. δst may also be a function of a steering angler speed,for improving a transient response of the vehicle motion. It should benoted that the steering gear ratio may be determined in other ways knownin the art.

For the stability control of suppressing understeering and oversteeringtendencies, the controller 34 monitors the deviation of the actual yawrate γ of the vehicle body from a target yaw rate γt, calculated usingoperational variables: a steering angle and a vehicle speed. The targetyaw rate γt is a value theoretically expected on the vehicle with givenoperational variables, and therefore the deviation, Δγ (=γ−γt), of theactual yaw rate γ from the target yaw rate γt indicates the degree ofthe deviation of the actual condition from the theoretically expectedcondition: the degree of deterioration of the vehicle behavior. Acounter yaw moment is generated to reduce the difference between theactual and target yaw rates by adjusting individual braking forcesand/or the steering angle of wheels. Accordingly, in the illustratedembodiment, the yaw rate is employed as a turning state parameter.

Target yaw rate γt may be given as a function of a vehicle speed V and asteering angle δb as follows:

$\begin{matrix}{{{\gamma\; t} = {{\frac{1}{\left( {1 + {\tau \cdot s}} \right)} \cdot \frac{1}{1 + {K_{h} \cdot V^{2}}} \cdot \frac{V}{H} \cdot \delta}\; b}},} & (2)\end{matrix}$where H is a wheel base; Kh, a stability factor; τ and s, a timeconstant and a frequency variable in Laplace transform. The detailedderivation of this formula may be found elsewhere.

With respect to the parameter δb of the steering angle in the expression(2), when no automatic steering is executed, an actual steering angle δamay be considered as coinciding with the provisional target steeringangle, δst, determined based upon the driver's handling with exp. (1).Thus, the actual steering angle δa may be used as the parameter δb inexp. (2) in absence of automatic steering.

However, if automatic steering for a stability control is once started,the actual steering angle δa is changed from the provisional targetsteering angle δst. In this case, a target steering angle δt that theturning angle varying apparatus 24 is commanded to accomplish is givenby:δt=δst+Δδt  (3),where Δδt is a modification of the steering angle in a stability controlfor suppressing a behavior deterioration. Accordingly, the actualsteering angle δa is not always consistent with the driver's handlingoperation. Thus, in the inventive device, during the execution of theautomatic steering for a stability control, the provisional targetsteering angle δst may be used as the parameter δb in exp. (2), andthereby rendering the driver's intention to be always reflected in thetarget yaw rate.

If any failure disabling automatic steering control occurs in thesteering apparatus or in the turning angle varying apparatus 24, theupper and lower steering shafts are mutually locked. In this case, sinceno further automatic steering is executed, the actual steering angle δawill be used as the parameter δb in exp. (2).

In this regard, if any failure disabling automatic steering controloccurs during the execution of the automatic steering for a stabilitycontrol, the parameter δb in exp. (2) will be switched from theprovisional target steering angle δst to the actual steering angle δa.However, this switching of the parameter δb could cause an abruptvariation of the target yaw rate value γt in exp. (2) because, usually,the actual steering angle δa coincides with δt (=δst+Δδt). Then, inorder to avoid such an abrupt variation of the parameter δb and thetarget yaw rate γt, an asymptotic (smoothing) process may be applied forthe parameter δb: the parameter δb is rendered to change gradually. Inrepetitive cycles of the control routine as described below with aflowchart in FIG. 2, the parameter δb is given by:δb=R·δ _(bn)+(1−R)·δ_(bn-1)  (4),where δ_(bn) is a steering angle parameter to be selected in a currentcycle and δ_(bn-1) is a steering angle parameter selected forcalculating the target yaw rate γt in the last cycle. R is a filteringfactor between 0 and 1, determined using a map in FIG. 4 as a functionof the vehicle speed V. As seen from the map and exp. (4), the effect ofsuppressing the variation of the parameter δb increases as the vehiclespeed increases because a larger variation in the target value should beavoid at a higher speed. According to the calculation (4), suppose theprovisional target steering angle δst has been selected as the parameterin a certain cycle and the actual steering angle δa is selected in thesubsequent cycle, δb is given by R·δa+(1−R)·δst. [δst in the last termmay be given by exp. (4) in the preceding cycle.] This smoothing processmay be always executed in repetitive cycles of the control routine.

The flowchart in FIG. 2 shows an exemplary control routine foraccomplishing the vehicle stability control in the inventive controldevice. In this embodiment, the automatic steering control independentlyof the driver's handling is executed [together with the adjusting ofbraking forces on the wheels] only when an oversteering tendency to besuppressed, or a spinning condition is detected. An understeeringtendency, if detected, is suppressed only through the adjusting ofbraking forces as in a usual vehicle stability control. This is becauselateral forces on front wheels of an understeering vehicle are oftenbeing saturated. Further, if any failure occurs in the steeringapparatus, no automatic steering control is executed. In such a case,the stability control is executed only through the adjusting of thebraking forces even when the vehicle is oversteering.

Referring to FIG. 2, the control routine may be started by a closure ofan ignition switch (not shown in FIG. 1) and cyclically repeated at acycle time such as milli-seconds during the operation of the vehicle.

In this routine, firstly, signals as described above are read-in (step10) and the provisional target steering angle δst is determined withexp. (1), using a map as shown in FIG. 3 (step 20). Then, in steps30-40, it is judged if any failure occurs in the steering apparatus(step 30) and if a stability control through the automatic steering isexecuted in the preceding cycle (step 40). As shown, when no failureoccurs and a stability control through the automatic steering isexecuted, the provisional target steering angle δst is selected as thesteering angle parameter δb to be used for the calculation of the targetyaw rate γt (Step 50). Otherwise, the actual steering angle δa isselected as the steering angle parameter δb (Step 60). The actualsteering angle δa may be directly measured with any appropriate sensoror estimated with the following:δa=(θ+θre)/Rg  (5)

Subsequently, in step 70, the smoothing process for the parameter ofsteering angle δb is executed using the expression (4) as describedabove, and the target yaw rate γt is calculated using the expression (2)in step 80.

Then, in steps 90, the degree of deterioration of the vehicle behavioris evaluated by judging if the absolute value of the difference of theactual and target yaw rates Δγ exceeds a reference value γo, a smallpositive constant. If no, no stability control is to be executed so thatthe provisional one δst is set for the target steering angle δt [and nobraking pressure adjusting is executed] (step 100).

If |Δγ|≧γo, indicating that the behavior deterioration is advanced,whether the vehicle is oversteering or understeering is judged in step110, e.g. by evaluating the amount of Δγ·signGy, where signGy is a signof the lateral acceleration. If Δγ·signGy>0, the vehicle isoversteering; otherwise, the vehicle is understeering.

If the vehicle is oversteering, the counter yaw moment Mt is calculatedin step 120 so as to reduce the deviation of the yaw rate Δγ, anddivided into two components: one, Mbt to be generated through theadjusting of the braking forces on wheels; and the other, Mst to begenerated through the automatic steering (in step 130). The division ofthe counter yaw moment may be done in one appropriate way realized byone of ordinary skill in the art. Then, in step 140, a target steeringangle modification Δδt is calculated and the target steering angle δt isgiven by the expression (3), so as to generate the counter yaw momentcomponent Mst.

On the other hand, if the vehicle is understeering, the counter yawmoment Mt is calculated in step 150 and the target steering angle δt isset to the provisional one δst in step 160 because no automatic steeringcontrol is executed in this case. Set for the counter yaw moment Mt willbe a yaw moment component, Mbt, to be generated through the adjusting ofthe braking forces on wheels.

Then, in step 170, modification amounts of braking pressures on therespective wheels ΔPbti (i=fl, fr, rl and rr) are calculated so as togenerate a yaw moment component Mbt in one appropriate way, realized byone of ordinary skill in the art.

Finally, the steering angle is adjusted to the target steering angle δt(step 180) and the braking pressure control is executed in steps 190 and200. In step 190, the braking pressure Pbti for each wheel may be givene.g. by:Pbti=Ki·Pm+ΔPbti  (6),where Pbti, Ki are a target braking pressure and a conversion factor foreach wheel, respectively; Pm, a master cylinder pressure. It should benoted that the control of braking pressure may be executed in any otherway known in the art as far as the component Mbt is generated. Steps 190and 200 may be executed prior to step 180.

After the execution of step 200, the control routine returns to theStart and the next cycle is started.

In the above-described routine, it should be noted that the provisionaltarget steering angle δst is selected as the steering angle parameter δbonly when the automatic steering control is executed in the precedingcycle. If no automatic steering control is executed or an automaticsteering control is ceased in the preceding cycle, the actual steeringangle δa is employed as the steering angle parameter δb for calculationof the target yaw rate γt.

In this connection, normally, the actual steering angle δa is renderedto be substantially coincident with the provisional target steeringangle δst. Thus, under normal conditions in absence of any failure, theprovisional target steering angle δst may be always selected as thesteering angle parameter δb. However, when a failure occurs in themotion of the steering apparatus, usually, the upper and lower steeringshafts are locked at any non-neutral position, i.e. the position ofθre≠0. In such a case, the provisional target steering angle δst cansignificantly differ from the actual steering angle δa. Thus, when anyfailure occurs in the steering apparatus, the actual steering angle δais always selected as the steering angle parameter δb.

Further, it should be noted that the selecting of the provisional targetsteering angle δst under execution of the automatic steering control canalso compensate for the mechanical delay in the actuation of thesteering apparatus during the automatic steering control. During theautomatic steering control, it is possible that the steering apparatusis requested to actuate the tie rods for the front wheels relativelyquickly (at a large amount per one cycle). In such a case, the motion ofthe actual steering angle δa could be delayed relative to the variationof the target steering angle δt. However, if the target yaw rate γt iscalculated with the provisional target steering angle δst, the delay ofthe motion of the actual steering angle δa will not contribute to thecalculation (Rather, the following-up action of the steering apparatuswill be improved).

Although the above routine is designed to always execute the smoothingprocess for the parameter δb, that process may be executed only afterthe switching of the parameter and/or the excessive variation of theparameter occur. However, normally, since the variations of the actualsteering angle δa and the modification amount Δδt are smooth, thevariation of the parameter δb is not excessively smoothed out.

Moreover, the routine may be designed to execute the automatic steeringcontrol and/or the adjusting of braking forces only when the magnitudesof the respective counter yaw moment components Mst, Mbt exceed thecorresponding reference values Msto, Mbto (>0) as shown in FIG. 5.

Although the present invention has been described in detail with respectto preferred embodiments thereof and some partial modifications thereof,it will be apparent for those skilled in the art that other variousmodifications are possible with respect to the shown embodiments withinthe scope of the present invention.

For instance, the inventive control device may be employed in a frontdrive vehicle and a four wheel drive vehicle. As a steering apparatus, afull steer-by-wire power steering system may be employed. Further, theautomatic steering control may be applied for steering rear wheels.

1. A device for controlling a behavior of a vehicle having a vehiclebody, wheels and a steering apparatus that can steer the wheelsindependently of a driver's steering operation by a steering wheel, thedevice comprising: a portion for calculating a provisional targetsteering angle for the wheels based upon an amount of a steeringoperation of the driver and a predetermined steering characteristic; adetector for detecting an actual value of a turning state parameter; aportion for calculating a target value for the turning state parameter;a portion for calculating a target turning state control steering anglefor the wheels for reducing a magnitude of a deviation of the actualturning state parameter from the target value for the turning stateparameter when the magnitude of the deviation is at or above a referencevalue; and a portion for controlling a steering angle of the wheelsbased upon a final target steering angle incorporating therein thedriver's steering operation, the predetermined steering characteristicand the reduction of the magnitude of the deviation of the actualturning state parameter from the target value for the turning stateparameter when the magnitude of the deviation is at or above thereference value; wherein the target turning state parameter calculatingportion calculates the target value for the turning state parameter byusing the provisional target steering angle as a parameter representinga steered angle of the wheels, and wherein the portion for controllingthe steering angle of the wheels based upon the final target steeringangle comprises a rotary motion modifying device incorporated in aportion for transmitting a steering rotary motion of the steering wheelby the driver, the rotary motion modifying device being adapted torelatively rotate an input portion and an output portion thereof.
 2. Thedevice according to claim 1, wherein, when the magnitude of thedeviation of the turning state parameter is lower than the referencevalue, the steering angle controlling portion controls the steeringangle of the wheels through the steering apparatus by using theprovisional target steering angle as the final target steering angle. 3.The device according to claim 1, further comprising: a detector fordetecting an actual steering angle of the wheels, wherein the targetturning state parameter calculating portion calculates the target valuefor the turning state parameter based upon the actual steering anglewhen no steering control of the wheels based upon the target turningstate control steering angle is executed.
 4. The device according toclaim 1, wherein the provisional target steering angle is a sum of asteering angle of the wheels corresponding to the amount of the steeringoperation of the driver and a control steering angle for accomplishingthe predetermined steering characteristic.
 5. The device according toclaim 1, further comprising: a portion for controlling braking anddriving forces in the respective wheels; a portion for calculating atarget amount of a stability control based upon the turning stateparameter deviation for reducing the magnitude thereof; a portion fordividing the target stability control amount into a target stabilitycontrol steering amount for steering the wheels and a target stabilitycontrol braking and driving force amount for operating the braking anddriving force controlling portion at a predetermined ratio; and aportion for calculating the final target steering angle based upon thedriver's steering operation, the predetermined steering characteristicand the target stability control steering amount; wherein the steeringangle controlling portion controls the steering angle of the wheelsbased upon the thus calculated final target steering angle through thesteering apparatus; and the braking and driving force controllingportion controls braking and driving forces in the respective wheelsbased upon the target stability control braking and driving forceamount.
 6. The device according to claim 5, further comprising: adetector for detecting an actual steering angle of the wheels; wherein,when the steering apparatus can not steer the wheels independently ofthe driver's steering operation, the target turning state parametercalculating portion calculates the target turning state parameter basedupon the actual steering angle, and the target stability control amountdividing portion assigns the target stability control amount only to thetarget stability control braking and driving force amount.
 7. The deviceaccording to claim 6, wherein, when the steering apparatus becomesdisabled from steering the wheels independently of the driver's steeringoperation during the calculation of the target turning state parameterbased upon the provisional target steering angle in the target turningstate parameter calculating portion, the variation of the turning stateparameter owing to the change of the steering angle used in calculatingthe target turning state parameter from the provisional target steeringangle to the actual steering angle is lessened.
 8. The device accordingto claim 7, wherein a degree of lessening of the variation in theturning state parameter is larger at a higher vehicle speed than at alower vehicle speed.
 9. The device according to claim 2, furthercomprising: a detector for detecting an actual steering angle of thewheels, wherein the target turning state parameter calculating portioncalculates the target value for the turning state parameter based uponthe actual steering angle when no steering control of the wheels basedupon the target turning state control steering angle is executed. 10.The device according to claim 2, wherein the provisional target steeringangle is a sum of a steering angle of the wheels corresponding to theamount of the steering operation of the driver and a control steeringangle for accomplishing the predetermined steering characteristic. 11.The device according to claim 3, wherein the provisional target steeringangle is a sum of a steering angle of the wheels corresponding to theamount of the steering operation of the driver and a control steeringangle for accomplishing the predetermined steering characteristic.